In direct iron-making processes, iron oxide sources such as iron ore and iron oxide are directly reduced into reduced iron with carbonaceous reductants (hereinafter referred to as carbonaceous materials in some cases) or reducing gas. In a known direct iron-making process, a feedstock containing iron oxide such as iron ore and a carbonaceous material such as coal is fed onto a moving bed included in a rotary hearth furnace; the iron oxide is reduced into iron with the carbonaceous material by heating the feedstock with burners and radiation heat; the reduced iron is carburized, melted, and then allowed to coalesce; the resulting reduced iron is separated from molten slag; and the resulting reduced iron is solidified into granules by cooling.
In order to efficiently produce reduced iron with a high degree of reduction, the inventors have proposed a technique for separately controlling the flow of atmosphere gas and the temperature in such a rotary hearth furnace including a prior heating/reducing zone and a subsequent carburizing/melting/coalescing zone by providing at least one partition between these zones.
In order to achieve further improvements, the inventors have continued to perform investigation. In particular, the inventors have studied to solve a problem that the degree of reduction is cannot be sufficiently increased due to oxidizing gas.
In the known processes, furnaces have furnace gas outlets, placed in appropriate sections of the furnaces, for discharging combustion gas because an increase in the content of oxidizing gases such as carbon dioxide and water prevents the increase of the degree of reduction, the oxidizing gases being generated from burners during combustion for heating. Since the combustion gas is discharged, air is pulled into the furnaces through spaces around feedstock-feeding units and/or reduced iron-discharging units in some cases. The inventors have found that the air inhibits the reduction of iron oxide.
The present invention has been made to solve the problem. It is an object of the present invention to provide a method for properly controlling the flow of gas in a furnace and also provide an apparatus for properly controlling the gas flow. The method and the apparatus are useful in preventing reduction from being inhibited by oxidizing gas.